If a person is in the left line, wishing to receive only the Light of Hochma, then he senses darkness because he lacks the Light of Hassadim. By contrast, if a person is in the right line, completely in the Light of Hassadim, then he has no desire for reception and doesn’t aspire to the Light of Hochma (the small state).
How can we connect these two opposite states of Hassidim and Hochma? Since a person is divided into these two halves without an ability to unite them, the intervention of a third force is necessary. This third force causes the two opposite states to clash so that a new action can begin.
The truth of the matter is that every action is a new birth in spirituality. It is a new state that didn’t exist before, and we don’t know how to perform it. In fact, it is impossible to perform it, since every action reveals our lack of connection with the Creator and our opposition to Him.
How do we step over this chasm and make the leap from corporeality into spirituality on each and every degree? This occurs after much preparation, when a force comes to us and awakens the serpent in us, which is the evil inclination helping us perform this leap.
(Note: This principle comes from Kitrug HaYareyach, which occurred on the fourth day of creation.)